Method of treating earth formations



Patented Nov. 6, 1951 2.51am usrnon or nas'rmo nan-m RMATIONS Paul H.Oardwell and Parke D. Muir, Tulsa, Okla...

assignors to The Dow Chemical Company, Midland, Micla, a corporation ofDelaware mi 1mm. Application m as. me. Serial No. 11.111

I Claims. (Cl- 103-28) The invention relates to methods of treatingearth formations, especially those penetrated by a bore hole such as adeep well drilled for oil or gas. It more particularly concerns animproved method of bringing about consolidation of loose earthformations but without complete blocking of the interstices to fluidflow.

In the copending application of one of us, via, Paul H. Cardwell, SerialNo. 636,272, filed De-' cember 20, 1945, there is disclosed a method ofconsolidating fluid permeable loose earth formations. such as thosepenetrated b a well. without complete blocking of the interstices tofluid flow. The method is based upon the injection into the formationspenetrated by the well of a liquid mixture of resin-forming ingredients,capable of reacting in situ to form a solid resin, and a liquid diluentsoluble in the mixture but not in the solid resin. Upon permeating theinterstices of the particles of the earth formation, the resinformingingredients in the liquid mixture react in situ to form a solid resin,coating the earth particles. and cementing them together. At the sametime, the liquid diluent, which is rejected from the mixture as theresin hardens, holds open the fluid passages between the resin coatedearth particles so that the treated formation remains fluid permeablealthough consolidated.

In the practical application of this method difiiculties are sometimesencountered as when the formations to be treated are traversed bychannels, fissures, or cracks. We have found that the earthconsolidation resin-forming liquid mixture enters the fissures,channels, and cracks in preference to the interstices between theparticles of the earth formation itself so that the liquid mixture maybecome lost in the formation without producing the desiredconsolidation. Heretofore, in the use of resin-forming liquids forproducing a sealing and cementing action in earth formations of deepwells, rather than consolidation without sealing, it has been proposedto add fillers of certain fibrous or lamellar materials to theresin-forming liquid mixtures so as to prevent their being uselcsslydrained away into the earth. Examples of fillers disclosed in U. 3.2,274,297 are shredded or powdered asbestos. hemp, sawdust, and wood.Lamellar fillers, such as fragmented cellophane, are disclosed in U..S.2,353,372. While the use of these fillerswith conventional resin-formingliquids in wells is generally successful when a sealing or cementingoperation-is performed, as when the mixture of filler and resin-formingliquid is introduced into a well hole to seal of! water or cementcasing.

2 for example, attempts to use these and like conventional fillers inthe aforesaid earth consolidation' resin-forming mixture, not intendedto produce fluid impervious seals, have not been successful.

The conventional fillers filter out and deposit as a filter cake notonly in the channels, fissures and cracks in the formation to beconsolidated but also upon the face of the fluid permeable portions ofthe formation between the openings of the channels, fissures, andcracks. The filter cake thus deposited becomes consolidated and being ofconventional fillers is then impervious to fluids, so that fluid flowfrom the formation into the well is blocked by the cake. Theconventional fillers thus cannot be used effectively with theaforementioned earth consolidation type of resin-forming liquids when itis desired to produce consolidation within the formation and therefromproduce fluid such as oil or gas.

It is the principal object of the invention to provide an improvedmethod of producing consolidation within an earth formation using anearth consolidating resin-forming liquid mixture of the type disclosedin the aforesaid copending patent application, which cements togetherthe loose particles of fiuid permeable earth without blocking fluid flowthrough their interstices, whereby excessive drainage of the liquidmixture into channels, fissures, and cracks is prevented. Other objectsand advantages will appear as the description of the invention proceeds.

Our invention is predicated upon the use, in conjunction with the earthconsolidating resinforming liquid mixture, as a filler, of a solidsubstance in granular form in two ranges of particle size, one beingcoarse and corresponding in size to the channels, fissures, and cracks,the other comparatively fine and corresponding in size to the particlesof the formation to be consolidated.

The coarse portion of the filler is so chosen that the particles will becarried into and form a bridge in the channels, fissures, and cracks. Aswill be understood in the art difl'erent formations may be channeled,fissured, or cracked to various extents so that the choice of coarsefiller will be'made accordingly. As a guide to this choice, we havefound that one of the following three general ranges of coarse particlesizes may be used in most instances to achieve the desired channel,fissure, and crack bridging. (1) For large size channels, the coarseparticles, for example, may have a size passing a No. 3 standard sievewhile being retained upon a No. 10 standard sieve. (2) For medium sizedchannels, the coarse 3 particles may have a size, for example, passingthrough a Number standard sieve while being retained on a Number 20standard sieve. (3) For finely channelled formations, the coarseparticles, for example, may be between about 20 and 60 mesh.

The fine portion of the filler comprises particles that are at least ascoarse as those of the unconsolidated formation to be consolidated.These particles usually range between a Number 40 and 200 standardsieve, and in some instances as much as 75 percent of the formation maypass a Number 200 and be retained upon a Number 350 standard sieve.

The particles of both the coarse and fine portions of the filler arerounded fragments preferably substantially equiaxed in shape such asthose of rounded cubical, near cubical or spherical form, the latterform being preferred, so as to obtain a maximum amount of interstitialspace for fiuid flow. The usual particle form of sand and fine gravel isgenerally suitable.

The proportion of coarse particles in the mixture of coarse and-fine mayvary from about 80 to 60 per cent of the whole filler mixture whichshould contain at least to 30 per cent of the aforesaid relatively fineparticles, that is particles having about the same size as the formationparticles. The balance of the filler may consist of particles in eitheror both ranges of coarse and fine size.

Oil and gas-bearing sands through which oil or gas passes to a welldrilled thereinto usually are composed of particles falling within afairly narrow range of particle sizes and can be consolidated by themethod of the aforesaid patent application. Table I sets forth thestandard sieve analysis of a few typical unconsolidated oil well sands.

TABLE I sieve analysis of typical unconsolidated oil well sands Percen eof Sample of Sieve Sire Given Bieve Mesh Size a Miocene Oligicine l riomm. named Sand Band Band Band Through a from from from from BarbersManuel Boling Boling Hill Field Field ram Field 4o 0. 4 a. s 1. o 4. a40 N 3. 9 2). 5 4. 5 17.2 00 an 25.0 54.1 42.4 41.1 so 100 as. 4 17. s29.1 21. o 100 200 so. a 4.1 an. 1 1a 1 zoo so as 1.1 M

In the foregoing table, the oil-producing sands exemplified are composedof particles more than 90 per cent of which pass through a 40 meshstandard sieve and are retained on a 200 mesh. In general, the sands orformations with which the invention finds its widest use are composed ofparticles at least 90 per cent of which are retained upon a 200 meshsieve while at least 80 per cent of those so retained pass through a 10mesh sieve.

As already indicated, the function of the filler used in accordance withthis invention is to prevent wastage of the earth consolidationresinforming liquid into channels. fissures. and cracks while permittinginjections of the liquid into the interstices of the unconsolidatedparticles of the formation and without producing a fluid imperviouscemented filter cake on the formation. To achieve this, we add to theearth consolidating resin-forming liquid mixture a granular filler thatis partly composed of' the particles having about the same size of thatof the unconsolidated sand and partly coarser particles. The coarserparticles bridge the openings into the channels. fissures, and crackswhile the finer particles, which simulate the formation itself, bridgethe interstices of the coarse particles of filler so that the deposit offiller or filter cake obtained is pervious to fluid and possesses aboutthe same size interstices as the formation.

The following examples tabulated in Table II are illustrative of fillermixtures composed of both coarse and fine particles. the former servingfor channel bridging and the latter for partly closing the bridgedpassages and keeping the interstices of the formation open to fluid fiowafter consolidation as aforesaid. Standard sieve numbers are used.

In the foregoing table Example No. 1, for instance. is typical of ascreen or sieve analysis of a filler generally suitable for formationshav-- ing large channels. In this example per cent of the filler iscomposed of relatively large particles, i. e. particles having a meshsize between about 0.25 inch and 0.1875 inch. The balance of the fillersimulates, in particle size, typical fiuid permeable earth formationsthe sieve analysis of which are given in Table I. The filler of Exampleis suitable for use with formations having channels of moderate size,while the filler of lihrample 3 is suitable for use in formations havingbut small sized channels or fissures.

The filler, comprising the mixture of coarse and fine particles, asabove described, may be mixed with a suitable liquid vehicle, e. g. oil,water. brine, and the mixture of vehicle and filler introduced into thewell so as to carry the filler particles into the channels. fissures,and cracks before introducing the resin-forming earth consolidatingliquid into the well and thence into the formation or the filler may bemixed with the earth consolidation liquid, and, using the latter liquidas the vehicle for the filler, the mixture introduced into the well. Wehave found that it is advantageous to employ about 0.25 to 1.0 pound offiller mixture for each gallon of liquid vehicle. After or during theintroduction of the filler in admixture with the liquid vehicle into thewell, pressure may be applied, if necessary, so as to force the fillerinto the channels, fissures, and cracks and form a cake on the face ofthe formation. When the liquid vehicle for the filler is the earthconsolidating resin-forming liquid, a quantity sufficient to impregnatethe formation to the desired extent is used. If the filler is conveyedtothe formation by another liquid. it is to be followed by theresin-forming liquid and asvaceo the amount of the latter liquid whichis used is governed by the same considerations as to the depth ofimpregnating it isdesired to produce. For example, we have gallons ofresin-forming liquid may be used per vertical foot of well hole in theformation to be treated.

Various solid substances may be used for the filler that have preferablyabout the same specific gravity as that of the liquid vehicle used toconvey'the filler to the earth formation. The specific gravity of theearth consolidation resin-forming liquid mixture aforementionedincluding the diluent lies between about 0.97 and 1.05. We have foundthat suitable solids which may be comminuted to the desired sizes andform of filler particles of suitable specific gravity are walnut shells,(sp. gr. 1.3), pecan shells, (sp. gr. 1.17), cocoanut shells, (sp. gr.1.43), gilsonite, (sp. gr. 104), solidified phenolaldehyde resins, (sp.gr. 1.20-1.30), and polystyrene, (sp. gr. 105-1.07). Other granulatedsolids may be used that have a specific gravity similarly approximatingtha of the vehicle.

The following example is illustrative of the preparation of an earthconsolidation thermosetting resin-forming liquid mixture which cementsfiuid permeable loose earth particles together at the temperaturesencountered in deep well formations without blocking the interstices tofluid flow.

Exurrns A 390 pounds of phenol are mixed with 506 pounds of 37 per cent(by weight) aqueous formaldehyde solution and 50 pounds of a 50 per cent(by weight) aqueous solution of caustic soda as a catalyst and themixture cooked at 175 F. until it attains a viscosity of about 8centipoises. This cooking requires about 2.5 hours. The cooked mixtureis treated with hydrochloric acid solution in amount sufficient toreduce the pH of the mixture to about 4. This requires about 62.3 poundsof 32 per cent hydrochloric acid. The addition of the acid results inthe formation of a two layer system, the water layer being rejected,leaving 64 gallons of resin-forming liquid having a viscosity of about300 centipoises. The resin-forming liquid is diluted with a liquiddiluent that is soluble in the resin-forming liquid but not in the resininto which the resin-forming ingredients in the liquid solidify whensuitably catalyzed. Examples of suitable diluents are: methyl alcoholand ethyl alcohol. As much as 1.5 volumes of the alcohol may be used foreach volume of the resin-forming liquid. When diluted with 1.5 volumesof methyl alcohol the specific gravity of the mixture is 0.99.

In using the mixture of resin-forming liquid and diluent therefor, toconvey the filler to the formation as well as consolidate it, about 0.25to 1 pound of filler above described are added per poimd of liquidvehicle, and. just before the mixture is to be injected into theformation to be consolidated a catalyst is added, such as an aqueoussolution of an alkali metal hydroxide or carbonate, which promotes thecondensation of the resin-forming ingredients in the resin-formin liquidinto a solid resin. The amount of catalyst used determines, at a giventemperature,the rate at which the resin-forming constituents in themixture condense into a solid resin. By using as a catalyst, apredetermined amount of the aqueous alkaline solution, known settingtimes may be had. As an example. a suitable catalyst is obtained bydissolving 275 pounds of potassium found that about to 50 a carbonateand 41 pounds of potassium hydroxide in 36 gallons of water. Thissolution added to the resin-forming liquid, prepared as above described.in the amount of 12.5 gallons of the alkali solution per gallons of theresin-forming liquid diluted with gallons of methyl alcohol causes theresin-forming ingredients in the mixture to set'into a solid resin in 4hours at F. At F., 5 gallons of the alkaline solution similarly usedproduces setting in 4 hours, and 1.5 gallons produces setting in 4 hoursat 210 F.

Other resin-forming liquid mixtures of the phenol-aldehyde type may beused which, upon dilution with a liquid diluent that is soluble in theliquid mixture but not in the resin formed therefrom, set to a solidresimcementing fluid permeable loose earth particles together withoutblocking the interstices to fiuid flow.

Exmru: B

The following is another example of a suitable diluted thermosettingresin-forming liquid which is composed of two diluted partiallycondensed phenol-aldehyde type resin-forming liquids. when suitablycatalyzed, the mixture sets to a solid resin cementing fiuid permeableloose earth particles but without blocking the interstices to fluidflow. It is especially useful in formations having a temperature belowabout 175 F. One of the two partially condensed resinforming liquids isprepared as follows: To 64 gallons of the resin-forming liquid ofExample A (before the addition'of catalyst and diluent) add 410 poundsof resorcinol and stir the mixture until the resorcinol is dissolved.There is thereby obtained 10'! gallons of the resin-forming liquid whichis then diluted with 160.5 gallons of methyl alcohol to make about 267.5gallons of a diluted resin-forming liquid mixture having a specificgravity of 1.02. It is designated L1. The other partially condensedresin-forming liquid is prepared as follows: Mix together 600 pounds ofcresylic acid (commercial), 500 pound of paraformaldehyde and 25 poundsof 50 per cent aqueous caustic soda solution and maintain the mixture atabout 130 F. until the paraformaldehyde dissolves. This paraformaldehydeusually dissolves in about 30 minutes. The dissolving reaction isexothermic and i conducted preferably in a conventional reaction'vesselprovided with cooling means so that the temperature of the reaction isprevented from exceeding the aforesaid temperature. After theparaformaldehyde is dissolved, the reaction mass is acidified to a ofabout 4 with hydrochloric acid. This may be accomplished by using 31.15pounds of 32 per cent (by weight) aqueous hydrochloric acid. Afterneutralization, there is obtained about 105 gallons of resin-formingliquid having a viscosity of about 100 centipoises. This resin-formingliquid is diluted with 157.5 gallons of methyl alcohol thereby producingabout 262.5 gallons of a diluted resin-forming liquid mixture having aspecific gravity of 0.98. It is designated L2.

The two diluted resin-forming liquid mixtures (L1 and L2) are mixed inequal volumes a aforesaid before use, the mixing being delayed untiljust before theearth formation is to be consolidated and then therequisite amounts of filler and catalyst are also added. The amount ofcatalyst used determines the setting time at a given earth temperature.As the catalyst there is used a 25 per cent by weight aqueous solutionof caustic soda. For example. to obtain setting and consolidation inabout 4 hours at 90 F. there asraeea is used 3 gallons of the aqueouscaustic soda solution per 100 gallons oi the equal volume mixture of L1and L2. At 150 F., 0.5 gallon sufllces to produce hardening in 4 hours.

The amount of catalyst solution to employ to obtain setting at othertimes and temperatures may be estimated by extrapolation andinterpolation from the foregoing data of setting temperatures andcatalyst proportions.

The following data in Table III illustrate the eii'ect on the fluidpermeability of consolidating the unconsolidated oil well sands of TableI using a resin-forming liquid mixture of Example 13. In these data, thefluid permeability of the sand before and after consolidation wasmeasured using as the earth consolidation resin-forming liquid mixtureequal volumes of L1 and L2 catalyzed with 3 gallons of 25 per centaqueous caustic soda solution per 100 gallons of the resin-formingmixture. The temperature of the consolidation was about 90 1". and about0.25 of a pound of ground walnut shells having the sieve analysi ofExample 1 was added to the earth consolidation resin-forming liquidmixture per 100 gallons thereof.

TABLEIII Permeability of oil well sands before and alter consolidationsimilar results to those in Table III are obtained upon using othersimilar diluted resinforming earth consolidating liquid mixturescontaining granulated filler having a proportion oi. about 30 to 60 percent of particles the same size as those of the formation to beconsolidated in admixture with a proportion of 15 to 80 per cent ofcoarse particles larger than those of the formation but small enough topass into and bridge therein the channels, fissures, and cracks.

Although the practice of the method has been exemplified moreparticularly in connection with I producing sands having lmconsolidatedparticles of a sieve size between a number 40 and 200. it is to beunderstood that the method may be practiced similarly on unconsolidatedformations of which up to 75 per cent of the particles pass a number 200sieve while being retained upon a number 350 sieve.

We claim: 1. The method of consolidating a channeled. flssured. orcracked fluid permeable earth formation consisting of earth .particlesat least 90 per promoting their condensation to a hard resin.

said mixture being diluted with a liquid soluble therein but not in theresin and carrying in suspension a filler consisting of rounded granulesof which by weight to 60 per cent exceed the sieve size oi the earthformation and pass a number 3 standard sieve, 15 to 30 per cent havesubstantially the same sieve size as those of the earth formation, thebalance of the filler particles having a sieve size between a number 3and 200,

the amount of said filler being from 0.25 to 1.0 pound per pound ofdiluted resin-forming liquid mixture.

2. The method according to claim 1 in which the diluent is methylalcohol.

3. The method according to claim 1 in which the diluent is ethylalcohol.

. PAUL H. CARDWELL.

PARKE D. MUIR.

REFERENCES CITED The following references are of record in the file ofthis patent:

- UNITED STATES PATENTS Number Name Date 2,146,480 Kennedy Feb. 7, 19392,206,877 Shepler July 2, 1940 2,221,261 Lehnhard, Jr Nov. 12, 19402,337,295 Kennedy Dec. 21, 1943 2,345,611 Lerch et al. Apr. 4, 19442,348,484 Lawton May 9, 1944.

